Yesterday we received a letter from Assembly member Daniel O’Donnell announcing that he had been sent the NYC Dept. of Buildings’ 808 Columbus Avenue Report of Investigation, dated Feb. 15, 2008, which looks into the retaining wall collapse last summer.
Below are some excerpts from that report, which I found linked from the Park West Village Tenants Association website and can also be found here.
The investigation concluded that the segment of sheeting system that collapsed was erected on top of a highly weathered (fractured) weak rock formation, and not on the competent rock indicated on the design drawings. Calculations showed that sheeting set upon a weathered rock base would eventually fail once the adjoining competent rock holding the weathered rock base in place was destabilized, whether by blasting or by mechanical means. On the date of the collapse, the adjoining rock was in fact removed by blasting. Prior to the blasting, this rock had provided lateral restraint to the weathered rock mass underneath the sheeting. The fragmentation of the adjacent rock allowed the weathered rock on which the sheeting had been erected to be displaced and thus induced the collapse (Pg. 1).
…
The lack of proper observations and stabilization measures by the responsible supervising engineer throughout pile installation and subsequent excavation allowed this failure to occur. If the rock under the sheeting had been competent, as indicated in the design drawings, or if the weathered rock had been stabilized as soon as it was identified either in the field or from a reading of the geotechnical report submitted by RA Consultants prior to the excavation, the fragmentation of the adjacent rock would not have caused the sheeting to fail and the incident would not have occurred (Pg. 2).
…
In addition, the failure to take seismic measurements appears to have violated Fire Department requirements. The failure to identify the weakened condition of the rock and the non-compliance with FDNY monitoring requirements should be referred to the appropriate units for issuance of violations or other appropriate action (Pg. 2).
The report also states, “The fractured and weakened condition of the rock mass could have been identified by the controlled inspector employed by Mayrich,” (Pg. 2) and that person could have informed Gotham Construction, the general contractor for the new building.
Also striking is the timeline of events of the days and hours leading up to the evacuation of the 784 Columbus Ave. and though the day the last residents were allowed back into the building. Two calls went to 311 between 1:30pm and 4pm, July 25, each with reports that the building was shaking. Police and the NYFD responded to a 911 caller shortly before 10pm, who reported the collapse, and the building was evacuated.
Blasting did significantly weaken the rock to which the protective sheeting (retaining wall) was secured, the report says, but there is insufficient evidence to conclude that blasting on July 25 was carried out improperly or directly caused further fragmentation of the rock, which ultimately lead to the collapse. The wall, and the building, sits atop the intersection of at least two fault lines in the rock. This could have contributed to the collapse.
I learned a lot about the local geology and proper blasting techniques and precautions from reading the report. It includes many nice pre- and post-collapse pictures of the site, too.
I appreciate being notified of the report’s existance. Thank you, sir. And thanks to the DOB for finishing the report in under seven months. (I know that sometimes reports seem to take forever to compete, and I’m not being sarcastic there.)





